Generally, there is a steering system in vehicles so that a driver changes moving direction of a vehicle. The steering system consists of: a steering wheel, installed at the front driver's seat and rotated by a driver; a steering column mounted on the bottom of the steering wheel; a gear box for changing tires direction with improved steering force simultaneously with converting rotational motion of the steering wheel into direct motion; and a universal joint for conveying turning force, delivered to the steering column, to the gear box.
The universal joint comprises a shaft joint, and a pipe joint configured to be slipped toward the shaft joint and deliver rotating torque.
There are serrations along the the longitudinal direction of the outer peripheral surface of the shaft joint, and there are splines, corresponding to the serrations, in the inside of the pipe joint. Thus, the shaft joint enables to deliver rotating torque while being linked to the pipe joint through gear combination and being slipped toward axial direction.
As above, when assembling the shaft joint and the pipe joint, a sliding cage, composed of a ball bearing, or combination of a ball bearing and a needle bearing, is mounted on the outer side of the end of the shaft joint so that the shaft joint and the pipe joint may be further elastically slipped.
Further, the surface of the bearing assembled to the sliding cage is covered with lubricants such as grease or oil, and the shaft joint is insertedly assembled to the inside of the pipe joint.
However, if the sliding cage is composed of a ball bearing, or combination of a ball bearing and a needle bearing, the universal joint may be smoothly slipped, but the ball bearing is in line-contact. Thus, dents may be generated in the shaft joint due to the ball and it causes noise generation or performance degradation of a steering apparatus in case of using the steering apparatus.
To overcome such problems, Patent Publication No. 10-2014-0039660, a prior art, has been suggested.
Instead of a ball bearing, the prior art is composed of a cylinder-shaped needle bearing for maintaining good steering condition as well as preventing dent generation of slip bush for rotating torque of the steering apparatus.
However, when a shaft joint of the needle bearing is slipped along the inside of a pipe joint or a universal joint is rotated by operation of a steering wheel, there is a problem that coefficient of friction is high because the whole outer side of the needle bearing is under surface-contact to the inside of the pipe joint.
Accordingly, since the universal joint is not smoothly slipped and rotated, it is not possible to maintain good steering feel of the steering apparatus.
Further, as duration of use of the steering apparatus is accumulated, the needle bearing is worn out due to frictional resistance and torque delivery. Thus, it causes performance degradation of the steering apparatus as well as noise generation since a gap of rotational direction of a steering wheel is getting larger when using the steering apparatus.